Treating wash oil



March 6, 1934. H. JONES 1,949,746

TREATING WASH OIL Filed Feb. 7, 1930 INVENTOR. Zr//7 #Jo/7615.

ZW G? dark and opaque.

Patented Mar. 6, 1934 ienne TREATING WASH OIL Irvin H. Jones, Pittsburgh, Pa., assigner to The Koppers Company of Delaware, a corporation of Delaware Applieation February 7, 1930, SerialNo. 426,585

2 Claims.

This invention relates to a process of treating cil and more particularly to a process of reconditioning wash oil used in the benzol recovery system of a gas or by-product coke-oven plant.

Fresh wash oil after introduction into the benzol recovery system, gradually increases in viscosity and in specific gravity, and changes from a light colored clear oil to one which is This change in the oil is due to the accumulation during the gas washing process, of organic compounds which are principally sulphur derivatives and which are of a deep brown color. These compounds dissolve Yto some extent in the wash oil and also exist in the oil in the form of a suspension or colloidal dispersion when the limit of the solubility in wash oil has been reached. r

t been found that the above organic materials are soluble in sulphuric acid and other acid substances such as sodium acid sulphate. Phosphoric acid may be used but it is not as satisfactory as sulphuric acid. The solubility increases with the concentration of the acid. The acid therefore serves as an effective extracting or ccagulating medium for'the removal of the aforesaid dark colored substances whether in solution cr in suspension.

The present invention is an effective and simple process for restoring dirty wash oil to approximately its original condition when introduced into the wash oil system. By removing a portion of the absorbent oil from the system at regular intervals and treating it with sulphuric to extract the accumulated undesirable matter, it is possible to extract the same more rapidly than it builds up in the system. In this Way the system may be kept fairly clean.

The oil used in most plants for benzol recovery is obtained from petroleum reneries essentially in the form of high boiling fractions of petroleum oil which have been puried by acid or other treatment. It is preferably one which yields about distillate up to 250 C., and

about 85% between 250 C. and 370 C.

The fouled Wash oil which is withdrawn from the wash oil system is mixed with sulphuric acid preferably of 50 to 66 B. From about 2% to by volume of acid or preferably 212% by 'l volume may be used.

'I dehydrated oil is then agitated for about fifteen minutes with the additional acid and permitted to settle for about ve minutes or more and the heavy sludge is quickly drained olf. During the extraction it is preferable to treat the oil at a temperature below 70 C., although satisfactory results are obtained at higher temperatures.

The acid in the clarified wash oil may be neutralized by adding sodium carbonate, caustic soda or other alkaline substance. Preferably a 10% solution of sodium carbonate is used, and enough of it is added to insure proper neutralization of the acid in the wash oil. If desired, the clarified wash oil may be agitated with about by volume of water before the addition of the alkaline solution.

The wash oil after it is clarified in the above manner may then be passed into the oil circulating system or to a storage tank.

The accompanying drawing serves to illustrate the manner in which the present process may be practiced.

The figure shown is an elevational View of a portion of a common light-gil recovery plant including additional pipe connections needed for withdrawing fouled wash oil and for replacing it with clean wash oil.

In accordance with the usual practice, gas from coke ovens, for instance, is passed upwardly through washers l and 2 successively in counter-current relation with wash oil which is sprayed in at the tops of the washers and, as the oil proceeds downwardly, it absorbs the light oil vapors from the gas, along with the undesirable sludge. The so-ealled benzolized wash oil is co1- lected in a tank 3 and is passed to a stripping still 4, after passing through a vapor-to-oil heat exchanger 5, an oil-to-oil heat exchanger 6 and a superheater 7.

The de-benzolized wash oil passes out of the bottom of the stripping still 4 through the oil-tooil heat exchanger 6 and to the hot de-benzolized wash oil tank 8. The latter oil is ordinarily prepared for re-use in the Washers l and L by pumping it through a cooler 9. A tank 10 serves as a storage tank for the cooled de-benzolized oil. A tank 1l serves usually for the storage of fresh Wash oil.

The light oil vapors from the stripping still 4, after passing through the heat exchanger 5, are condensed in a cooler 12. The light oil then passes into a decanter 13 and a tank 14, from which it is passed to a crude still (not shown) for separation into the usual products.

In the present process, the fouled wash oil icc iid

may be withdrawn for treatment from the wash oil circulating system at any convenient point. As shown in the drawing, it may be withdrawn from the hot de-benzolized wash oil tank 8 by means of a pipe 16 or it may be withdrawn from the cooled de-benzolized wash oil tank 10 by means of a pipe 17.

For the purpose of treating the fouled wash oil, an agitator 15, such as that ordinarily used in a light-oil plant for treating light oil fractions, may be used. The fouled wash oil is pumped to the agitator 15, where it is clarified in accordance with the present process. A tank 19 may serve as an acid supply and a tank 20 as an alkali supply.

The sludge and water layers formed in the agitator 15 may be drained out and disposed of through a pipe 21. The clarified wash oil may be passed into a tank 22 through a pipe 23. A pipe 24 serves to return the clarified wash oil to the wash oil circulating system. For this purpose, the pipe 24 may be connected with the cooled debenzolized wash oil tank 10 or with the fresh wash oil tank 11, or both.

In some light oil plants, the cold oil circulating tank 10 communicates with a cold oil decanter tank not shown in the drawing, which in turn communicates with a sludge tank likewise not shown. In this case the sludge from the sludge tank may be pumped to the agitator 15 and treated in the manner described above, although when the process is working efficiently the sludge tank and the cold oil decanter may be dispensed with.

The following examples are given to illustrate more specifically the process of the present invention.

Example 1.--About 4,800 gallons of used wash oil, the temperature of which is about 50 C., are Withdrawn from the wash oil circulating system and pumped to the agitator. The oil is later treated with about 25 gallons of 66 B. sulphuric acid to dehydrate the same. After settling, the acid layer is withdrawn. The oil is then agitated for about 15 minutesI with 120 gallons of 66 B. sulphuric acid and permitted to settle for about 10 minutes. The sludge is drawn oii and the oil is washed with about 250 gallons of water. This Washing is followed by the addition of about 100 pounds of soda ash dissolved in 155 gallons of water.

The oil and the alkaline solution are agitated for about 10 minutes and permitted to settle for about 11/2 hours. A very good separation is obtained at about C. The clarified wash oil is then ready for re-use in the wash oil circulating system.

Example 2.-About 5,000 gallons of used wash oil, the temperature of which is about 42 C., are

r agitated for about 15 minutes with about 20 gallons of 66 B. sulphuric acid to dehydrate the oil. The mixture is permitted to settle for about 2 hours, after which the water and soft sludge are withdrawn. This is followed by another treatment with about 120 gallons of 66 B. sulphuric acid. The mixture is permitted to settle for about five minutes and the sludge is drawn on". The acid treated oil is then washed successively with water and with an alkaline solution prepared by dissolving 100 pounds of soda ash in 150 gallons of water. After proper settling and separation the clarified oil is ready for use in the wash oil circulating system.

The dehydration step included in the above examples is not always necessary. If the wash oil is withdrawn from a point in the system where settling is likely to take place, it will have a low water content in which case the dehydration step may be omitted.

The present method may be very easily adopted in any benzol recovery plant without the installation of much additional equipment. In fact it has been found that with the addition of a few extra pipe lines the process may be successfully carried on.

After the above treatment the wash oil is in as good a condition as when first introduced into the system as fresh oil. The removal of the accumulated organic material greatly improves operating conditions in the oil circulating system in that stoppage is prevented and the oil is rendered more highly absorptive.

I claim as my invention:

1. A method of reclaiming fouled wash oil free of light oil which has been used for scrubbing light oil from fuel gas and which originally consisted of petroleum fractions none of which boil substantially below 250 C. which comprises treating said fouled wash oil at a temperature below "10 C. with about 2 to 10% of its volume of 60 to lll: 66 B. sulphuric acid whereby the said oil is clarified, removing the sludge formed in the oil by such treatment, washing with water and aqueous solution of alkali, thereby to remove the acid from the clarified wash oil.

2. A method of reclaiming fouled wash oil free of light oil which has been used for scrubbing light oil from fuel gas and which originally consisted of petroleum fractions none of which boil substantially below 250 C. which comprises treating said fouled wash oil with about 1/2 of 1% of I-IQSOr to dehydrate the oil, thereafter treating the oil at a temperature below 70 C. with about 2 to 10% of its volume of 60 to 65 B. sulphuric acid whereby the said oil is clarified, removing 13C* the sludge formed in the oil by such treatment, washing with water and aqueous solution of alkali, thereby to remove the acid from the clarified wash oil.

IRVIN H. JONES. 

